Percutaneous transluminal coronary angioplasty (PTCA) is used to increase the lumen diameter of a coronary artery partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. Typically a first guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the first guidewire to a point just proximal of the stenosis. The first guidewire is then removed. A balloon catheter on a smaller 0.014 inch diameter second guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The second guidewire is advanced into the stenosis, followed by the balloon on the distal end of the catheter. The balloon is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. It has also been shown that the use of intravascular stents can measurably decrease the incidence of restenosis after angioplasty thereby reducing the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel reclosure. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in diameter from small coronary vessels of 3 mm or less to 28 mm in the aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A typical stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A typical stent 10 ranges from 5 mm to 50 mm in length. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. Stents radially expand as the balloon is inflated, forcing the stent into contact with the interior of the body lumen thereby forming a supporting relationship with the vessel walls.
Various shapes of stents are known in the art. U.S. Pat. No. 4,886,062 to Wiktor for "Intravascular Radially Expandable Stent and Method of Implant" discloses a two-dimensional zig-zag form, typically a sinusoidal form.
U.S. Pat. No. 4,856,516 to Hillstead for "Endovascular Stent Apparatus and Method" discloses a wire first bent into a series of tight bends. The wire is then further bent into a sequence of loops that are connected by half hitch junctions and interconnections which are either aligned or spiral around a circumference of the stent.
U.S. Pat. No. 4,878,906 to Lindemann et al. for "Endoprosthesis for Repairing a Damaged Vessel" discloses a flexible, plastic, thin-walled sleeve molded with various types of circumferential and axial ribs and reinforcements to be used as an endovascular prosthesis.
U.S. Pat. No. 4,994,071 to MacGregor for "Bifircating Stent Apparatus and Method" discloses a wire forming a backbone extending axially along the length of the lattice that extends away from the lattice and is used to construct the interconnecting loops.
U.S. Pat. No. 5,133,732 to Wiktor for "Intravascular Stent" discloses a stent body coiled from a generally continuous wire with a deformable zig-zag structure with a means for preventing the stent body from stretching along its longitudinal axis.
The above art discloses various axial ribs. The disadvantage of such single longitudinal reinforcements is that of reduced flexibility. What is needed is a stent design which controls the length of the stent as it expands on a balloon yet maintains flexibility without resulting in longitudinal compression at the center of the stent when expanded.